Domain redirection in .htaccess

Since the domain mapping plugin is not able to handle all the situations we need I'm going to remove it and just use domain aliases (as per Rackspace's definition) and .htaccess redirection to take care of everything we need to. I've got most of it working, but for some reason I can't figure out (and neither can Rackspace support, although it's not their forte) the non-www version of the redirection domain is not working. So I'm hoping there is a mod_rewrite guru here who can help.

Here's my situation:
- WP Multisite installation using directory structure.
- Each blog will have 2 unique domain names that point to it (redirect to it)
- One of these domain names (the .us domain) will be the main domain we want to optimize SEO for

Here's an example:
Blog's real address is: http://domain.us/blogA. Redirect rules go into this site's .htaccess file.

Unique domain http://www.blogA.us set up as alias pointing to http://www.domain.us, this domain becomes the main domain all SEO efforts are directed towards. Redirection must keep http://www.blogA.us in the browser address bar.

Unique domain http://blogA.com set up to catch everyone who automatically types .com after a name. Should redirect to http://www.blogA.us so that browser address bar changes to http://www.blogA.us as 301 redirect.

Currently I've only got my test case set up using one domain got it working for http://www.blogA.us. But when I try it with http://blogA.us it's not working. Instead it redirects to http://www.domain.us (where the alias is pointing). Before I go any further and complicate things by adding in the redirection for the http://www.blogA.com and http://blogA.com domain redirects I want to get this working. Ultimately I do need the code for the whole scenario to work with both .us and .com names and both www and non-www versions of each domain name.

Whew. So... mod_rewrite gurus, help please!